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Poor Longwall Productivity and Claystone Roof Rock: A Need for Geotechnical Analysis.
Paper in Proc 1989 :21-26
Longwall failures can occur when shield supports are used in inappropriate strata conditions. This U.S. Bureau of Mines paper is a case study of one such failure. Shield rotation resulted in poor longwall production rates in a mine with fractured claystone roof rock. The fractured claystone, with abundant fossilized root casts, was further weakened by its tendency to swell upon contact with mine air at the longwall face. The immediate claystone roof rock crushed between an overlying massive, cantilevering main roof rock and the stiff shields. The loss of confinement in this low tensile and shear strength roof rock was aggravated by the use of four-leg shield supports. These factors have combined to cause the claystone roof rock to disintegrate into small blocks. These blocks then became dislodged and fell onto the conveyor. This action created an irregular roof surface for the shields to pressurize against, causing them to rotate out of position. Straightening rotated shields caused extensive production delays. Solutions to the problem consist of utilizing shield designs that best support this type of rock or avoidance of these areas by longwall mining techniques. Advanced planning to utilize these solutions could be accomplished with progressive geotechnical techniques prior to the selection of equipment and the start of mining. The matching of appropriate mining systems with specific strata conditions can minimize the unanticipated instability problems and greatly diminish the potential for future longwall failures.
Paper in Proc., 1989 Multinational Conf. on Mine Planning & Design; Univ. Kentucky, 1989, PP. 21-26